1. June 21, 2012 Submillimeter Spectrum of Chloromethane: Analysis of the V 3 =1 Excited State Presented by: Alissa Fisher Auburn University and U.S. Army Aviation and Missile Research, Development, and Engineering Center Presented to: International Symposium on Molecular Spectroscopy Approved for Public Release; distribution unlimited. Review completed by the AMRDEC Public Affairs Office 20 Apr 2012: FNS884 Reference herein to any specific commercial, private or public products, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement, recommendation, or favoring by the United States Government

2. 2 FileName.pptx CH 3 Cl Spectroscopy Two isotopomers CH 3 35 Cl and CH 3 37 Cl Methyl halide with a large permanent electric dipole moment Prolate symmetric top with threefold degeneracy Follows selection rules ∆J= +-1 and ∆K=0 Hyperfine splitting is visible I = 3/2 quantum number F= I+J Does not occur naturally **T. W. Pape. (1993). Collisional Processes in Methyl Chloride. (Doctoral Dissertation). Duke University. J µ K 1000 Energy (cm -1 ) V3V3 J’’ J’ K K F F 0

3. 3 FileName.pptx V 3 =1 is associated with the stretching of the C-Cl bond Numerous studies of the ground state and V6 level exist V 3 is 4kT above the ground state –Less intense by a factor of e -4 based on Boltzmann statistics Rotational Spectra of the V 3 =1 Energy Level Population fractions of the three most populated vibrational states. Vibrational State Energy (cm -1 ) DegeneracyPopulation Ground 0195.553% V3V3 732.8812.677% V6V6 1018.0721.337%

4. 4 FileName.pptx Powerful source of CW THz radiation THz laser based on laser- induced rotational population inversions in GS, V 6 Inversion is collisionally quenched –Depopulating V 6 rapidly is critical to OPFIR laser performance Principal vibrational relaxation mechanism is from V 6 to V 3 to Ground –DR Spectroscopy can measure the rate of this* OPFIR Laser * As presented by D. J. Phillips/ IR/THz Double Resonance Spectroscopy Energy Dynamics at Atmospheric Pressures/ /UAH. 2012. 1000 Energy (cm -1 ) V3V3 0 Ground State V6V6 1018 cm -1 0 cm -1 J10 K6 J11 K6 J12K6 J11 K7 l1 J12 K7 l1 J13 K7 l1 9R12 CO 2 Laser Line Relaxation pathway

5. 5 FileName.pptx Previous work –Thorough analysis of V 3 with IR spectroscopy which involves measured lines up to J=62-63, K=19* unable to resolve hyperfine Use of ground state terms for the higher order distortion constants –Hyperfine constant eQq was fit with measured lines up to J=10-11, K=10 using microwave spectroscopy** Current work –Predictions off by a few MHz –Measurement from J=5-6, K=0 up to J=25-26, K=12 –Higher order parameters necessary for accurate prediction of line centers at high resolution Background Constant 112 CH 3 35 Cl 12 CH 3 37 Cl B 3 /MHz 13177.6387 (12) 12975.8168 (13) D J /kHz 18.1302 17.6065 D JK /kHz 199.0172 193.684 H J /Hz -0.013 -0.0108 H JK /Hz 0.246 0.29 H KJ /Hz 9.623 9.2 L J /mHz -- eQq/MHz -74.809 (45)-59.058 (45) *M. Betrencourt / JOURNAL OF MOLECULAR SPECTROSCOPY 128,433-443 (1988 ) **G. Wlodarczak/ JOURNAL OF MOLECULAR SPECTROSCOPY 116,25 1-255 (1986)

6. 6 FileName.pptx Experimental Setup Virginia Diodes Inc. (VDI) frequency tunable Schottky diode source and detector Four multipliers spanning a region of 140 GHz to 750 GHz –WR – 5.1 (140-220 GHz) J5-7 –WR – 3.4 (220-330 GHz) J8-11 –WR – 1.5 (330-500 GHz) J12-18 –WR – 2.2 (500-750 GHz) J19-27 Vacuum Chamber Detector Methyl Chloride Vacuum Manifold Terahertz Source

7. 7 FileName.pptx Data acquisition utilizes modulation spectroscopy and lock in detection To maximize resolution and signal strength –Measurements made at pressure where Doppler and pressure broadening were equal –Depth of modulation was set at Doppler width Experimental resolution is ± 50 kHz Modulation Spectroscopy

8. 8 FileName.pptx Data CH 3 35 Cl J=23-24, K=12 CH 3 37 Cl J=9-10, K=7 0 0.2 0.4 0.6 0.8 1.0 -0.2 -0.4 259.25 259.255 259.260 259.265 CH 3 35 Cl J=9-10, K=9

9. 9 FileName.pptx Transition Frequency

10. 10 FileName.pptx Results J transitions from 9 to 25 of the K=9 levels J transitions from 12 to 25 of the K=12 levels Deviation of measured line centers Vs. Theoretical line centers using older constants plotted with the deviation using the newer constants. O-C (kHz) J Lower

11. 11 FileName.pptx Analysis SPFIT is used for fitting transitions and term values Constant 112 CH 3 35 Cl New 12 CH 3 37 Cl (New) B 3 /MHz 13177.6387 (12)13177.64324 (19) 12975.8168 (13)12975.8078(172) D J /kHz 18.130218.1372(10) 17.606517.6065(98) D JK /kHz 199.0172199.1587(23) 193.684193.470(173) H J /Hz -0.013-0.00756(23) -0.0108-0.0435(204) H JK /Hz 0.2460.359(6) 0.29.1525(250) H KJ /Hz 9.6239.46(10) 9.29.213(17) L J /Hz - 0.00000265(17) -0.000000305(12) eQq/MHz -74.809 (45) -74.857(29) -59.058 (45) Fits include J=0-1, K=0 up to J=25-26, K=12

12. 12 FileName.pptx V 3 =1 has been examined by a frequency tunable microwave source with Schottky diode multipliers and detectors in the submillimeter region. Doppler limited spectra was obtained for J <25 and K<12 for both Chlorine isotopomers. New hyperfine, quartic, and sextic rotational constants for the V 3 =1 were fitted Special Thanks To: DANE J. PHILLIPS, Kratos Defense and Security Solutions Digital Fusion, 4904 Research Dr., Huntsville, Al, 35805; DENNIS G. WILSON, Massachusetts Institute of Technology; ELIZABETH RHODES, University of Alabama Tuscaloosa; HENRY O. EVERITT, Army Aviation and Missile RD&E Center, Weapon Sciences Directorate, Redstone Arsenal, AL, 35898. Conclusion